The University of Oxford’s coronavirus vaccine stimulates broad antibody and T cell responses, published trial results show.

Researchers published further data from phase one/two clinical trials of the ChAdOx1 nCoV-19 Covid-19 vaccine, showing the evidence for the decision to move to a two-dose regimen in ongoing phase three trials.

The data also shows how the vaccine, developed with AstraZeneca, induces broad antibody and T cell functions.

Previous studies have shown that in order to develop any vaccine against SARS-CoV-2 coronavirus, two key elements of the immune system need to be activated.

These are neutralising antibodies against the coronavirus spike protein which is likely to be critically important in protecting against the disease, as well as robust T cell responses.

The findings are reported in two papers, both released in the peer-reviewed journal Nature Medicine.

Professor Katie Ewer, a lead author of one of the papers, said: “This highly detailed analysis of the immune responses to ChAdOx1 nCoV-19 further underpins the potential of this vaccine to induce protection against Covid-19 disease and provides additional reassurance of the safety of this approach.

“Using these advanced immunological techniques, we can better understand the different cellular and antibody-mediated mechanisms that contribute to the protection afforded by this vaccine, as demonstrated in the recent data from the subsequent phase three trials.”

One paper outlines the early-stage planning involved in the design of phase trials to investigate two booster dose schedules – a standard dose followed by a second standard dose and a standard dose followed by a lower dose.

The researchers show lower reactogenicity (eg sore arm) to either booster dose, and increased immune system responses.

This data was used to support the change to a two-dose regimen in the ongoing phase three trials.

The booster doses of the vaccine induced stronger antibody responses than a single dose, with the standard dose/standard dose inducing the best response – supporting the decision to move to a two-dose vaccine regimen in phase three trials.

The paper also shows that many different antibody functions are triggered by the vaccine that may be important in protection from the disease.

But if the antibodies cannot not stop a virus from entering the body, T cells can kill infected cells.

In the second paper, the authors detail an investigation of the T cell and antibody responses generated by the vaccine.

They report that the proteins – known as cytokines – which allow T cells to generate signals to the rest of the immune system, produced by the immune system in response to the vaccine, predominantly induce Th1 cytokines rather than Th2 cytokines.

The authors further report induction of a T cell subset, known to be particularly effective at clearing virus-infected cells from the body during infection.

This type of T cell response in combination with the detailed antibody profile is highly favourable for an efficacious vaccine, and further supports the profile of this vaccine as safe, researcher say.